Full automatic coffee makers constructed as shown in FIGS. 6 and 8 have heretofore been known which combine the functions of grinding coffee beans and causing boiling water to drip over the ground coffee, the dripping function automatically starting immediately after the coffee beans have been ground. The coffee maker constructed as shown in FIG. 6 has a vessel 1 in which a coffee grinding compartment and a filtering compartment for brewing coffee and separating the brewed coffee and coffee grounds from each other are integrally formed. Within the interior of the vessel 1 there is provided a cutter 3 rotatably driven by a driving motor 2. A filter 4 for separating brewed coffee and coffee grounds is provided at the bottom of the vessel 1. Coffee is brewed in this coffee maker in the following manner: after coffee beans have been ground by the cutter 3, water contained in a water reservoir 5 is introduced through a check valve 6 into a water pipe 8 formed integral with a heater 7, and is heated thereat. Hot water is then pumped up by virtue of steam pressure generated from the heated water to a discharge pipe 8' positioned above the vessel 1, and is poured therefrom into the vessel 1.
In a coffee maker constructed in this manner, the cutter 3 is rotated at high speed to generate a large centrifugal force at the time of grinding coffee beans. Since a filter member, if disposed on the peripheral wall of the vessel 1, is immediately damaged by this operation, such filter member or filter 4 must be disposed at the bottom of the vessel where it can be kept relatively free from the effect of the centrifugal force. In terms of the material of the filter 4, a mesh type filter 4 made of stainless wire is employed in place of filter paper which is commonly used in brewing coffee, since such filter paper would easily be damaged at the time of grinding.
Generally, in order to brew a delicious coffee, it is essential to grind coffee beans to a suitable particle size and to reduce an amount of fine powder (having a particle size of smaller than 48 mesh) in the ground coffee. Also, it is essential to brew the thus ground coffee with hot water, which has once been boiled, at a temperature ranging between 92.degree. C. and 96.degree. C. for about 3 to 4 minutes. In order to complete brewing in three to four minutes, it is a deciding factor to provide an adequate capacity for a filter member, to form an appropriate filtering layer in the ground coffee by pouring hot water on the ground coffee to swell the same well, and to gently and continuously pour hot water on the ground coffee without stirring the filtering layer. Grinding carried out in the construction described above presents a state of high speed grinding in a closed space represented in engineering of pulverization to produce a large amount of fine powder. In the construction described above, the filter 4 has a small area of filtering and ground coffee clogs the mesh of the filter 4 at the time of grinding while a large amount of fine powder fills up the gaps among particles of coffee, so that time required for filtering becomes quite long with the result that it usually takes seven to twelve minutes to brew five cups of coffee.
In the above-described hot-water supplying system, it is not possible to raise the temperature of water to an adequate degree. This system exhibits the characteristics shown in FIG. 7 and relating to temperature of hot water supplied and brewed coffee relative to. In FIG. 7, the curvatures shown by a and b denote temperatures of supplied hot water and brewed coffee while c designates brewing time.
For this reason, the coffee brewed by the coffee maker shown in FIG. 6 proves unpalatable. Furthermore, it becomes muddy because of the finely ground coffee beans contained therein.
A coffee maker shown in FIG. 8 includes a coffee bean grinding compartment 9 and a filtering compartment 10 for brewing coffee and separating this brewed coffee from coffee grounds by means of a filtering material such as a paper filter, the grinding and filtering compartments being constructed separately. The grinding compartment 9 receives a cutter 12 rotated by a driving motor 11. A perforated portion 13 for discharging ground coffee is provided on a part of the peripheral wall of the grinding compartment 9. The perforated portion 13 and the filter compartment 10 communicate with each other through a transfer pipe 14, so that, when coffee beans are ground within the grinding compartment 9 to a suitable particle size, the ground coffee is sequentially discharged through the perforated portion 13 onto a filter 15 disposed in the filtering compartment 10. Upon completion of this discharge, coffee is brewed by the same principle as that of the coffee maker shown in FIG. 6.
Although the coffee maker shown in FIG. 8 is improved in terms of the generation of fine powder at the time of grinding and the filtering capacity of a filter material as compared with the coffee maker shown in FIG. 6, no improvement has been made with respect to the temperature of hot water supplied during the brewing and the brewing time. It also suffers a serious problem in terms of operability. Generally, coffee beans contain a large amount of fats, and they therefore become sticky when ground. In consequence, all the coffee ground in the grinding compartment 9 is not discharged to the filtering compartment 10, a part of it adhering to the inner wall of the transfer pipe 14. When brewing coffee, steam generated during the brewing enters the transfer pipe 14 and is condensed therein, thus preventing the adhered coffee from leaving the transfer pipe 14. As grinding of coffee beans and brewing of coffee are repeated, the transfer pipe 14 may become clogged, eventually leading to the suspension of its discharging function. To solve this problem, the coffee grinding compartment 9 must be removed and washed everytime it is used. However, such washing is often not conducted, and the large number of parts to be cleaned makes this cleaning troublesome. The coffee which has been ground is discharged at a high speed, so that when it is once discharged on the filter material 15 disposed in the filtering compartment 10, it may bounce and scatter, thereby causing a part of the ground coffee to enter the gap between the filter material 15 and the filtering compartment 10 and to become mixed with the brewed coffee.